The use of red phosphorus as a flame retardant of polymeric materials is widely described, in the patent literature, according to which red phosphorus powder is employed in percentages depending on the nature of the polymeric material, generally in admixture with coadjuvant substances.
It is also known that red phosphorus, in the open air, reacts with oxygen and water vapor, so evolving, besides oxygenated acids, also phosphine, which is known to be very toxic, what results in a serious drawback for the above-mentioned use of red phosphorus, both, and chiefly, during the incorporation of same into the polymeric materials, as the relevant operative conditions, particularly the molding step, magnify the aforesaid undesired phenomenon to such an extent as to prevent said technical use of red phosphorus, and during the storage and handling which precede such incorporation.
Many processes have been described in the past, which aimed at stabilizing red phosphorus powder against phosphine forming by mixing or encapsulation of this powder with various materials, such as, for example, potassium silicate, silver nitrate, aluminium hydroxide, copper sulphate with copper chloride, condensates of bisphenol A with cyanuric chloride, magnesium or aluminium salts of ethylenediamine-tetra-acetic acid, chlorinated waxes, liquid chlorinated paraffins, melamine, melamine resins, phenol-formaldehyde resins, epoxy resins, polyacrylonitrile etc.; the known processes, however, exhibit the drawback of providing an insufficient stabilization to phosphine forming.